[Physical and imaging properties of heavy metal filter combinations in chest radiography]

We have investigated the performance characteristic of the heavy metal filters with higher atomic numbers by comparing their patient exposures, tube loadings, radiographic contrasts, and noise Wiener spectra with those of a combination of copper and aluminum filter which has been used widely in chest radiography. Seven heavy metal filters were used for this study. As for a tungsten filter, two filters different in thickness were used. One is 0.05 mm thick, and the other 0.10 mm. The other metal filters were respectively combined with a tungsten filter with a thickness of 0.05 mm. Among the all filters investigated, tube loading of tungsten filter with 0.05 mm thick is minimum. Tungsten with 0.1 mm thick and tungsten with 0.05 mm+ barium show the larger advantages in patient exposure than those of the other filters. It was found that the magnitude of patient exposure varied slightly with the difference of image receptor used. The use of heavy metal filters showed the small advantages in the patient exposure reduction ( approximately 20%) compared with that of conventional copper filter. The use of heavy metal filters showed increasing tube loading ( approximately 5 times) compared with that of conventional copper filter. Noise Wiener spectra of heavy metal filters showed comparable with those of conventional copper filter. In conclusion, the use of heavy metal filter combinations offer no significant advantages over optimal conventional filters.